Indicator papers



Unite States Patent "7..

INDICATOR PAPERS Henry Wenk er, Bradenton Beach, Fla.

No'Draw'ing. Application July 20, 1959 Serial No. 828,026

4 Claims. (Cl. 23253) The purpose of this invention is the improvement of the fastness to water of chemical pH indicator papers which contain dyes of the class of 2-4-dinitrobenzene-azo naphtholsulfonic acids as indicators. Test papers prepa'red with these indicators, which belong to the group of acid wool dyes and possess no affinity to cellulose fibers, lose the indicator, in contact with a test solution, rapidly into the solution, thereby making the accurate reading of the pH value of the test solution diflicult or impossible; and when the indicator paper is treated with a test drop, the rapid spreading of the drop carries away some of the indicator leaving a whitened center area, and the test is consequently 'vitiated.

It has now been found that these diifiiculties can be overcome if, in addition to the indicator, specified amounts of certain high-molecular organic bases are incorporated in the paper. This result is new and unexpected because high-molecular organic bases, although widely proposed as dye-fixing agents for increasing the water-fastness of substantive dyes, have until now not been proposed for artificially creating an afiinity to cellulose fibers with dyestutfs, such as acid wool dyes, which posses no natural aflinity whatsoever to cellulose fibers.

An extensive study of this new eir'ect showed that, although nearly all organic bases containing more than eight carbon atoms are capable of producing'the desired result of fixing the non-substantive indicator on filter paper, a majority of the bases produce undesirable sideefiects, such as impairing the storage stability of the paper or changing the clear yellow color which the indicator shows in an acid medium, to a dull orange or red color. Out of the large experimental material, only four groups of organic bases, all of them belonging to the class of quaternary ammonium bases, emerged which produced test papers of excellent stability and high sensitivity combined with very good fastness to water; their description will be found below in the examples and the appended claims.

In its practical application, the invention may be carc-ied out by impregnating filter paper with an indicator solution, drying, impregnating with a solution of a neutral salt of the organic base, such as the acetate or sulfate, and drying again. In at least one instance both the indicator and the base salt can be dissolved together in an organic solvent such as methanol without causing mutual precipitation, and in this case the process can be carried out in one operation.

Indicator papers prepared according to the invention lose little or no indicator upon immersion in distilled water during the first minute and only traces during the next four minutes. For comparison, an indicator paper containing the indicator 2-4-dinitro-6-sulfobenzene-azo-1- naphthol-6-8-disulfonic acid as sole ingredient without use of a dye-fixing base, loses all of the indicator and turns white upon immersion in distilled water in less than one minute. The sensitivity of the treated papers is the same as with the untreated papers, i.e. a complete change of the normally green test paper to yellow or blue, respec- 2,915,373 I Pat nted Dec. 1, 1959 'four "dye-fixing bases 6f the patent are interchangeable and work approximately equally well with the indicators referred to if used in theproper amounts. In the examples and in the appended claims, indicator-base ratios ar'efstated-which have been' found to work satisfactorily without, however,-precluding the use of somewhat 'rnodi fied ratios.

The following examples are illustrative, but by no means limitative of the invention (all parts being expressed in terms of weight unless otherwise indicated):

Example 1 Chem Anal. Edition, 1935,.pa'ge 40-41, are dissolved in 800 parts methyl alcohol.

(c) 'Filter paper is then impregnated with'this solution and dried. The paper has a green color which changes to blueon contact with alkaline solutionsTofpI-l 8.5 or higher and tofyellow on contactwithacid solutions of pH 5.5 or lower.

Example 2 (*a) 24.1 :par ts offhexadecylamine, 100 parts of 2- ethoxyethanol, 15 parts of anhydrous'sodium carbonate and 50 parts of dimethylsulfate are heated, with mechanical agitation, for 1 hour to 100 C. The resulting product, which now contains 30.1 parts of trimethylhexadecyl ammonium hydroxide, is dissolved in water, neutralized with sodium hydroxide and diluted to a concentration of 0.22 percent of ammonium base.

(b) Filter paper is then impregnated with a 0.2%

aqueous solution of the azo dye 2-4-dinitro-6-sulfobenzene-azo-l-naphthol-S-sulfonic acid which is described in Ind. Eng. Chem, Anal. Edition, 1935, pages 40-41, and dried.

(c) The paper is then impregnated with the solution of (a) and again dried. The paper has a green color which changes on contact with alkaline solutions of pH 8.0 or higher to blue, and with acid solutions of pH 5.5 or lower to yellow.

Example 3 (a) 12.5 parts of 25% aqueous methylamine solution, 30 parts 2-ethoxyethanol, 9.2 parts epichlorohydrin and 6 parts anhydrous sodium carbonate are heated for 3 hours to -88 C., with mechanical agitation. To the reaction product is added 12.6 parts dimethylsulfate; after standing for 12 hours the product, which now contains 11.9 parts of an ammonium base of the formula:

probably in the form of a high-molecular polymerate, is dissolved in water and diluted to 7500 parts, which means a concentration of 0.160% of ammonium base.

(b) Filter paper is impregnated with a' 0.2% aqueous solution of the azo dye 2-4-dinitro-6-sulfobenzene-azo-1- naphthol-6-8-disulfonic acid which is described in U.S. Patent No. 2,806,023, and dried.

(c) The paper is then impregnated with the above ammonium base solution (a) and again dried. The paper is of a green color which changes in contact with alkaline solutions of pH 7 or higher to blue, with acid solutions of pH 5.5 or lower to yellow.

Example 4 (a) 19.4 parts piperazine hydrate, 30 parts 2-ethoxyethanol, 9.2 parts epichlorohydrin and 6 parts anhydrous sodium carbonate are heated with mechanical agitation 3 hours to 90 C. After cooling, 25.2 parts dimethylsulfate is added at a temperature not exceeding 40 C. After standing for 12 hours, the product, which now contains 20.6 parts of an ammonium base of the formula:

. CHr-CH: CH:

CH:CHOHCHr-N q CHr-CH: OH

probably in the form of a high-molecular polymerate, is dissolved in 10,000 parts water, which means a concentration of 0.206% of ammonium base.

(b) Filter paper is impregnated with a 0.2% aqueous solution of the azo dye 2-4-dinitrobenzene-azo-l-naphthol-3-6-disulfonic acid which is described in U.S. Patent No. 1,975,340, and dried.

(c) The paper is then impregnated with the base solution (a), and dried again. The paper, olive green in color, changes in contact with alkaline solutions of pH 7 or higher to blue, with acid solutions of pH or lower to yellow.

This application is a continuation-in-part of application Serial No. 727,039, filed April 8, 1958, now abandoned.

I claim:

1. A pH indicator paper embodying the dye 2-4-dinitro-6-sul-fobenzene-azo-l-naphthol as indicator and the quaternary ammonium base obtained by the reaction of equirnolecular amounts of ricinoleic acid, N,N-diethyl- 1,3-propanediamine and dimethylsulfate and used in form of a neutral salt, as dye-fixing agent, with the amount of ammonium base being 1.3 parts for 1 part of indicator.

2. A pH indicator paper embodying the dye 2-4-dinitro- 6-sulfobenzene-azo-1-naphthol-8-sulfonic acid as indicator and the quaternary ammonium base trimethylhexadecyl ammonium hydroxide, used in form of a neutral salt, as dye-fixing agent, with the amount of ammonium base being 1.1 part for 1 part of indicator.

3. A pH indicator paper embodying the dye 2-4-dinitro- 6-sulfobenzene-azo-1-naphthol-6-8-disulfonic acid as indicator and the quaternary ammonium base CH3 CH:CHOHCH:r-N

obtained as a polymerate by the action of equimolecular amounts of methylamine, epichlorohydrin and dimethylsulfate and applied in form of a neutral salt, as dye-fixing agent, with the amount of ammonium base being 0.8 part for 1 part of indicator.

' 4. A pH indicator paper embodying the dye 2-4-dinitrobenzene-azo-1-naphthol-3-6-disulfonic acid as indicator and a polymerate of the quaternary ammonium base CHPCHz CH:

CHr-Cr OH obtained by the reaction of 1 mol piperazine, 1 mol epichlorohydrin and 2 mol dimethylsulfate and applied in form of a neutral salt, as dyefixing agent, with the amount of-ammonium base being 1.03 parts for 1 part of indicator.

References Cited in the file of this patent UNITED STATES PATENTS 1,975,340 Wenker Oct. 2, 1934 2,229,155 Wenker Jan. 21, 1941 2,806,023 Wenker Sept. 10, 1957 FOREIGN PATENTS 758,199 France Jan. 11, 1934 845,207 France Aug. 16, 1939 661,749 Germany June 28, 1938 722,281 Germany July 7, 1942 894,237 Germany July 8, 1949 

1. A PH INDICATOR PAPER EMBODYING THE DYE 2-4-DINITRO-6-SULFOBENZENE-AZO-1-NAPHTHOL AS INDICATOR AND THE QUATERNARY AMMONIUM BASE OBTAINED BY THE REACTION OF EQUIMOLECULAR AMOUNTS OF RICINOLEIC ACID, N,N-DIETHYL1,3-PROPANEDIAMINE AND DIMETHYLSULFATE AND USED IN FORM OF A NEUTRAL SALT, AS DYE-FIXING AGENT, WITH THE AMOUNT OF AMMONIUM BASE BEING 1.3 PARTS FOR 1 PART OF INDICATOR. 